Some fibrous material of plant origin comprises fiber and volatile organic material among other components. The volatile organic material is desireable as it can be used in the manufacturing of valuable products.
At the present time standard apparatus and process for separating the volatile organic material from the fiber and other components comprises a batch distillation process. An example is the isolation of mint oil from mint hay or the isolation of a volatile organic material (mint oil) from fiber and other components in the mint hay.
The mint oil is distilled out of mint hay. A tank measuring about 18 feet long, 71/2 feet wide and 6 feet tall is taken out into the field of mint hay. The tank contains steam lines in the bottom. In the field the mint hay is chopped and blown into the tank.
Then, the tank is taken from the field to the still and the steam lines in the bottom of the tank are connected to the steam lines from a large boiler. For a tank of this size the minimum size boiler is about 600 horsepower.
The steam from the boiler is introduced into the mint hay through the steam lines in the bottom of the tank. The mint hay in the tank is cooked for about one and one half hours. An approximate breakdown of the time required is that it takes about 20 to 25 minutes to force the steam through the mint hay in the tank. Then, for about another 20 minutes there is a good flow of a mixture of steam and mint oil to the condenser. After this 20 minute period of a good flow of a mixture of steam and oil from the mint hay in the tank the amount of oil coming off with the steam decreases for about 45 minutes. At that time the operator considers that he is spending more money on the fuel than he is receiving mint oil and the operation is not profitable. Therefore, the flow of steam to the tank is terminated and the tank is removed from the still. The residue from the mint hay, after the volatile mint oil has become a vapor and passes from the tank with the steam, is dumped into long piles and these long piles are later spread on the fields. At the present time two or three tanks of mint hay are, simultaneously, cooked.
The mixture of steam and volatile mint oil flows from the tank, as a vapor, to a condenser. In the condenser the vaporous mixture of mint oil and steam is condensed into a liquid mixture of water and mint oil. This liquid mixture of water and mint oil flows to a settling tank. The mint oil and water are immiscible and the mint oil, being of a lesser specific gravity than the water, rises to the top of the water and is drawn off into barrels. The mint oil is then ready to be shipped to a place of destination such as for use as mint flavoring in gum.
In the batch process for separating the volatile mint oil from the mint hay there is used about one gallon of diesel oil to distill and remove one pound of mint oil from the mint hay. It is estimated that in the year 1980 that there was distilled about 4,894,000 pounds of peppermint oil and 2,214,000 pounds of spearmint oil for a total of about 7,108,000 pounds of mint oil. In the midwestern part of the United States natural gas is used in the distillation process to fire the boilers to generate steam. However, the vast majority of the batch distillation processes use diesel oil to fire the boilers to generate steam for the distillation step. This can be interpreted to mean that in the year 1980 about 7,108,000 gallons of diesel oil were used to fire the boilers to generate steam to separate the volatile mint oil from the mint hay.
One of the reasons the use of diesel oil is so high, approximately one gallon of diesel oil for each pound of mint oil separated from the mint hay, is that the large steel tank is not insulated. With such a large steel tank not being insulated, there is a large surface area for the heat energy to be radiated away from the tank and also to be taken away by convention of air flowing over the surface of the tank. The large steel tank is moved and while being moved the insulation is damaged. The cost of repairing the damaged insulation is so expensive that a tank without insulation is used.